This invention relates to a touch sensitive panel in a hand held computing device.
Touch sensitive panels, referred to as xe2x80x9cinput screensxe2x80x9d herein, are widely used for hand held devices, including personal digital assistants, radiotelephones and other handheld wireless devices. An input screen with a resistive overlay (e.g., indium tin oxide) includes upper and lower transparent input layers positioned above a display screen, such as an LCD array, where each input layer includes two electrodes and a sequence of parallel, electrically resistive paths between the two electrodes. For a conventional touch panel, the upper layer is flexible and the lower layer is relatively inflexible, often being constructed from glass or a hard plastic. When a user uses a stylus or other appendage to touch the input screen at a selected location, the upper and lower input layers contact each other, generating a signal that identifies an x-coordinate (horizontal) and a y-coordinate (vertical) for the touched location relative to the display screen image. A conventional input screen requires at least four wires, one for each electrode, positioned between upper and lower input layers, to provide reference voltages and/or to transfer location information signals from an electrode to electronic components that process these signals. A conventional input screen will group all four wires as a unit and will route the wires along several edges of the input screen to the appropriate electrode. The device usually has one relatively inflexible tail that includes the four wires. The tail is usually bulky and requires provision of additional room around the input screen in which to fit the tail.
One result of this approach is that presence of the tail requires provision of a relatively large, non-usable border, referred to herein as a xe2x80x9crouting zonexe2x80x9d, on one or two sides of the four sides of the input screen, to provide room for the tail. A second result of this approach is that the portion of the device housing that surrounds the input screen is non-symmetric, being noticeably wider on each of one or two sides than on the opposite side(s). A third result is that the key area (bounded by the four electrodes; the region where the alphanumeric characters and graphics appear on the display screen) of the input screen is reduced substantially, by as much as 10-14 percent, relative to the input screen key area that would be available if the four-wire tail were not present. A fourth result of this approach is that the tail, when received within the device housing, is relatively inflexible and cannot be easily reconfigured to fit into the routing zone for wiring of the input screen and other components.
What is needed is an approach that (1) reduces the width of a routing zone that must be allocated to a tail within the device housing, (2) allows an increase in the input screen key area, (3) allows a reduction in one or more dimensions of the device housing without increasing any other dimension of the device housing, and (4) allows the key area to appear in a symmetric and more pleasing arrangement as part of the device housing.
These needs are met by the invention, which in one embodiment divides a four-wire tail into two or more tails, each carrying one or two wires, that are routed within the routing zone around the input screen in a more symmetric arrangement. Two of the four electrodes provide separate reference voltages used to operate the input screen. In one embodiment, a four-wire tail is divided into first and second two-wire tails, with a first tail serving the top electrode and the left-hand (or right-hand) electrode and a second tail serving the bottom electrode and the right-hand (or left-hand) electrode. The first and second two-wire tails are arranged to lie along the left side and right side, respectively, of the input screen, or along the top side and the bottom side, respectively, of the input screen. Because each two-wire tail has approximately the same routing width, which is reduced relative to the width consumed by a single four-wire tail, the input screen key area is or can be made symmetric relative to the device housing; and this size of the key area is increased compared to the size of the key area that would be available where a single four-tail must be accommodated within the routing zone. Alternatively, one or more dimensions (length and/or width) of the device housing can be reduced using the invention, relative to the corresponding dimension(s) of a housing with a conventional four-wire connector tail, without increasing any other dimension of the device housing.
In another embodiment, the four wires are replaced by three wires, where two wires are required to provide reference voltages. The wires are attached to the input screen at different locations so that one or more wires is positioned along each side (left, right, top and bottom). This allows use of reduced routing zone width along the sides and an increase in key area for the input screen.